/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.j2objc.annotations.WeakOuter;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NavigableSet;
import java.util.Set;

/**
 * A skeleton implementation of a descending multiset. Only needs {@code forwardMultiset()} and
 * {@code entryIterator()}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible(emulated = true)
abstract class DescendingMultiset<E> extends ForwardingMultiset<E> implements SortedMultiset<E> {
    abstract SortedMultiset<E> forwardMultiset();

    private transient Comparator<? super E> comparator;

    @Override
    public Comparator<? super E> comparator() {
        Comparator<? super E> result = comparator;
        if (result == null) {
            return comparator = Ordering.from(forwardMultiset().comparator()).<E>reverse();
        }
        return result;
    }

    private transient NavigableSet<E> elementSet;

    @Override
    public NavigableSet<E> elementSet() {
        NavigableSet<E> result = elementSet;
        if (result == null) {
            return elementSet = new SortedMultisets.NavigableElementSet<E>(this);
        }
        return result;
    }

    @Override
    public Entry<E> pollFirstEntry() {
        return forwardMultiset().pollLastEntry();
    }

    @Override
    public Entry<E> pollLastEntry() {
        return forwardMultiset().pollFirstEntry();
    }

    @Override
    public SortedMultiset<E> headMultiset(E toElement, BoundType boundType) {
        return forwardMultiset().tailMultiset(toElement, boundType).descendingMultiset();
    }

    @Override
    public SortedMultiset<E> subMultiset(E fromElement, BoundType fromBoundType, E toElement, BoundType toBoundType) {
        return forwardMultiset().subMultiset(toElement, toBoundType, fromElement, fromBoundType).descendingMultiset();
    }

    @Override
    public SortedMultiset<E> tailMultiset(E fromElement, BoundType boundType) {
        return forwardMultiset().headMultiset(fromElement, boundType).descendingMultiset();
    }

    @Override
    protected Multiset<E> delegate() {
        return forwardMultiset();
    }

    @Override
    public SortedMultiset<E> descendingMultiset() {
        return forwardMultiset();
    }

    @Override
    public Entry<E> firstEntry() {
        return forwardMultiset().lastEntry();
    }

    @Override
    public Entry<E> lastEntry() {
        return forwardMultiset().firstEntry();
    }

    abstract Iterator<Entry<E>> entryIterator();

    private transient Set<Entry<E>> entrySet;

    @Override
    public Set<Entry<E>> entrySet() {
        Set<Entry<E>> result = entrySet;
        return (result == null) ? entrySet = createEntrySet() : result;
    }

    Set<Entry<E>> createEntrySet() {
        @WeakOuter
        class EntrySetImpl extends Multisets.EntrySet<E> {
            @Override
            Multiset<E> multiset() {
                return DescendingMultiset.this;
            }

            @Override
            public Iterator<Entry<E>> iterator() {
                return entryIterator();
            }

            @Override
            public int size() {
                return forwardMultiset().entrySet().size();
            }
        }
        return new EntrySetImpl();
    }

    @Override
    public Iterator<E> iterator() {
        return Multisets.iteratorImpl(this);
    }

    @Override
    public Object[] toArray() {
        return standardToArray();
    }

    @Override
    public <T> T[] toArray(T[] array) {
        return standardToArray(array);
    }

    @Override
    public String toString() {
        return entrySet().toString();
    }
}
